The Global Positioning System (GPS) and similar satellite navigation systems (collectively, position, velocity, and time (PVT)) orbiting thousands of miles above the Earth have made possible determination of position and velocity by processing precise timing signals, to the benefit of consumer, commercial and government users alike. PVT signals are, however, quite weak when they reach the ground, making them easily disrupted by inadvertent or intentional interference as well as making them of little use in buildings.
Loss of PVT reception can cause navigation errors that increase operating costs and risk of accidents. As a result, various alternative and supplementary means have been proposed to improve the reliability and safety of instrument guided navigation. Active sensors, such as terrain following radar, do not require PVT or other radio frequency (RF) reference signals but impose cost and power burdens that severely limit their use. In response to such burdens, considerable time and money have been spent in efforts to create low cost and reliable passive instrument guided navigation technology.
Other than PVT, existing passive navigation relies primarily on image recognition, other RF signals and inferential sensors. Image recognition depends on visibility of previously mapped topography, limiting the conditions and areas where it can be used. RF reference signals where they exist are, like PVT, subject to interference and spoofing, reducing their value for instrument guided navigation. Waypoint navigation using magnetic field maps has been proposed but the cost of generating and continually updating such maps to compensate for field changes is prohibitive.
The most commonly used inferential sensor is the inertial measurement unit (IMU) which estimates position by double integration of trajectory disturbance signals. Unfortunately, such processing creates fast growing, unbounded errors. And, IMU are insensitive to constant forces, e.g. cross winds, which can create large cross track errors.
In light of the above, we disclose passive magnetic sensing means of determining position and velocity (PV) without requiring precise timing signals or maps.
Objects
A first object of the subject matter described herein is determining position of a platform, such as an airplane, submarine, or automobile. A second object is determining velocity through a magnetic field. A third object is determining a magnetic field signal. A fourth object is normalizing velocity for variation in magnetic field. A fifth object is registering position with respect to known location. A sixth object is platform navigating. A seventh object is forming magnetic field map.